Various rheometric devices are available to measure viscosity and transient flow phenomena. In a number of such devices, a fluid is positioned between two generally parallel members, one of the members is moved parallel to the other member, and the resulting force exerted upon the member which is not moved is measured. In this manner the viscometric properties of the entrapped fluid can be measured.
In recent years there has been a constant proliferation of new rheometrical techniques and commercially manufactured test devices. Various geometrical configurations have been developed for studying viscoelastic fluids, such as sliding plate and cylinder, capillary, slit, couette, cone and plate, fiber spinning, sheet inflation and other complex flows. Paralleling these advances in experimental capabilities has been the development of network and reptation theories to describe the rheological properties of polymer melts and concentrated solutions. Particular emphasis has been placed on the behavior of such systems in transient flows. Theoretical development has in turn created further stringent demands on instrumentation. This trend of increasing sophistication of modeling and experimentation has been stimulated by the constant attempt to elucidate the complex dynamics of viscoelastic fluids in order to improve the design and control of polymer processing operations.
Prior art designs for making the appropriate shear measurements have generally not been adequate to provide the reproducible shear measurements which are required to keep up with the development in theory.